Electron gun



July 14, 942 l v K ZWQRYKlN 2899952 ELECTRON GUN Filed Nov. 28, 194:0-

Patented July 14,1942

l wee Vladimir K. zwo'rykin, Philadelphia; Pa., assigner r 'to Radio Corporation of America, a. corpora- 'tion of Delaware Application November 28, 1-91170, Seriall No. 367,606

6 Claims. (Cl. 25M- 162) This invention relates to an electron gun and particularly to an electron gun which employs an ultra high frequency generator and ultra high frequency potentials, derived from the generator, for accelerating the electrons as they pass along a linear path.

Electron guns create beams of electrons which are accelerated as they pass alongva path toward the object on which they are directed. The electron acceleration may be aiiected by steady potentials or by .varying or alternating currents of proper phase. As electron velocities are y increased, it becomes more diiiicult to supply direct currents. i,

The present invention has for one of its objects the provision of means for establishing an electron beam of high velocity. AAnother object is to provide ',means for generating ultra high rfrequency currents and for applying forces derived from said currents to ,accelerate an electron beam; Another object is to provide means whereby ultra high frequency waves may be established with a resonant cavity provided with electron accelerating sections for establishing a high velocity electron beam.

The invention will be described by referring I to theaccompanying drawing in which Figure 1 y is a sectional view and schematic circuit diagram of one embodiment of the invention; Figure 2A is a sectional view along line II-II; and Figure.3 is a sectional view along line IIL-III.

Referring to Fig. l, a *.fluted cathode C, grids G, GG, and resonantcavty member l are arranged within an evacuated envelope 3. The cavity member may also act as the envelope. ihe cavity walls are extended adjacent the grids and cathode to form anodes A, AA. An auxiliary grid 2 may be used to phase the electrons leaving an auxiliary cathode E. In addition to the extensions for the anodes, ns 5 are alternately extended from the cavity Walls to support a plv rality of apertured members AI, A2, A3, A4, a5 to AN. rlhe apertures in these members are preferably coaxially arranged within the resonant cavity so that they are aligned with a projection E on the cathode. The relative lengths of the several apertures are important and will be described hereinafter.

The cathode is energized in any suitable maninclude thejelements of an electron microscope,

or anyobjectto be bombarded by electrons'.V

The aperturesin the members` AI to AN are of lengths L, L3, L4, L5, and LN, respectively. These lengths aresuch that an electron entering one of the apertures, with exception of the last. AN, with the maximum possible velocity f 1era/es it a lhalf period later, where 'a half period equals half the period of oscillation of the resonant cavity. :The operation of the device is as follows: vThe grids G, GG,.are coupled capacitatively to the anodes AAA,' respectively, and are biased so that electroncurrent to the anodes'is suppressed except when the latter have a potential, relative to thevcathode,l less than thev applied D. C. po-

ential. Infthis mannen. electron movements transfer energy fromthe D; KC.' supply to create and maintain standing waveA oscillations in the resonant cavity. ABy way of4 example,v with ran `applied D. C. potential of 15,000 volts, an oscillfator'y voltage of about 13,000 volts amplitude may be yestablished in the standing. waves inv the An electron beam, weaker than the anode currenti, will proceed from the cathode projection E along the axis of the cavity passing through'the apertures AI to AN. The electrons of this beam `will be accelerated through twice the voltage amplitude of the standing wave oscillation vin passing from one aperture tothe next. Inl the Iirst vaperture AI, this will bev 15,000 volts plus 13,000 volts or 28,000 volts, and'in the subsequent 54,000 volts; A3=54,00'0}26,000=80,000 volts; A4=80,000+26,000:106,00o volts; and A5: 106,000+26,000=132,000 volts. The iinal aperture AN may be of lesser length.

The lengths may be determined from the equation .Mv/2c, where A is the wave length, o the velocity of the electron, and c the velocity of light. Thus, it may 'be shown that for )\=40 centimeters, Ll=.16 \=6.2 cms; L2=.2l}\=8.6 cms; L3=.25 10.0 cms; L4=.28 \=11.2 cms; and L5=.30 \=l2.1 cms. These lengths may be varied to obtain the maximum acceleration if the phase variations along the length deviate in practice from the theoretical. Assuming 10% efficiency an output of one milliampere at 100,000 volts would require an input of one kilowatt or a mean anode current of '70 milliamperes, which can be obtained with a cathode including utings of about 0.15 centimeter in width and 2 centimeters in aggregate length.

Thus, the invention has been described as an electron gun in which a relatively low D. C. potential is converted into an oscillatory potential. The oscillatory potential appears along a resonant cavity as a Iuncticn of the standing waves established therein. These potentials are applied to members containing coaxially aligned apertures so that the electrons of a beam passing therethrough are accelerated as theypass from one aperture to the next succeeding one. The apertures are arranged with increasing lengths to phase properly the electrons so that the energy delivered to them increases the electron velocity. The device may be used as the electron gun of an electron microscope, cathode ray tube, or in any device in which high voltage electrons are required.

I claim as my invention:

1. In an electron gun, a member including a l resonant cavity, cathode, grid and anode electrodes arranged within said cavity, means including said cavity and said electrodes for converting direct currents into oscillatory standing wave potentials appearing within said resonant cavity, members including apertures arranged along the axis of said cavity and connected there.- to so that said potentials are applied to said apertures, and means including said cathode for directing an electron beam through said apertures so that the oscillatory potentials of said apertures increase the velocity of the electrons passing therethrough.

2. In an electron gun, a member including a resonant cavity, a iluted cathode, anode electrodes arranged on either side of said cathode, grid electrodes intermediate said cathode and anodes, said cathode, anodes and grids being located at one end of said cavity, means including said cavity and said electrodes for converting direct currents into oscillatory standing wave potentials appearing within said resonant cavity, members including apertures arranged along the axis of said cavity and connected thereto so that said potentials are applied to said apertures, and means including said cathode for directing an electron beam through said apertures so that the oscillatory potentials of said apertures increase the velocity of the electrons passing therethrough.

3. In an electron gun, a member including a resonant cavity, cathode, grid and anode electrodes arranged within said cavity, means including said cavity and said electrodes for converting direct currents into oscillatory standing wave potentials appearing within said resonant cavity, members including apertures arranged along the axis of said cavity and connected v thereto so that said potentials are appued to said apertures, said apertures increasing in length as the distance from the cathode increases, and means including said cathode for directing an electron beam through said apertures so that the oscillatory potentials of said apertures increase the velocity of the electrons passing therethrough.

4. In an electron gun, amember including a resonant cavity, cathode, grid and anode electrodes arranged within said cavity, means including said cavity and said electrodes for converting direct currents into oscillatory currents appearing as standing waves in said cavity, a plurality of members including apertures located substantially on the axis of said cavity and connected thereto, and means including said cathode for directing a beam of electrons through said apertures so that oscillatory potentials corresponding to said waves delli, er energy to increase the velocity of the electrons of Ysaid beam.

5. In an electron gun, a resonant cavity member, a pair of anode electrodes forming a part of said cavity member and disposed opposite each other at one end thereof, a cathode positioned between said anodes and spaced therefrom, a pair of grid electrodes located, respectively, between said cathode and anodes. said cathode including an electron emissive portion oriented for the emission of an electron beam along the axis of said cavity, and a plurality of apertured members connected alternately to the walls of said cavity along longitudinal lines, respectively, passing through the junction of the anodes and said cavity, said apertures being coaxially aligned along said axis.

6. In an electron gun, a resonant cavity mem'- ber, a pair of anode electrodes forming a part of said cavity member and disposed opposite each other at one end thereof, a iiuted cathode positioried between said anodes and spaced therefrom, a pair of grid electrodes located, respectively, between said cathode and anodes, said cathode including an electron emissive portion on the surface remote from said anodes and adjacent said cavity for the emission oI an electron beam along the axis of said cavity, and a plurality of apertured members connected alternately to the walls of said cavity along longitudinal lines respectively passing through the junction of the anodes and said cavity, said apertures being coaxially aligned along 'said axis, the lengths of said apertures increasing as the distance from said cathode increases up to the final aperture.

VLADIMIR K. ZWORYKIN. 

